Tandemly repeated sequences known as satellite DNA (satDNA) generally exhibit complex evolutionary patterns of concerted evolution in which mutations are homogenized and fixed in a stochastic process of molecular drive. Here, the nucleotidic variability of the MspI satDNA family of the pinewood nematode Bursaphelenchus xylophilus is analyzed in order to understand the evolutionary dynamics of satDNA at the intraspecific level. A total of 425 MspI monomer units, either PCR-amplified from isolates of local (Peninsula of Setúbal, Portugal) or worldwide origin, or retrieved from the B. xylophilus genome sequence, were characterized and compared. Whatever their origin, sliding window analysis of sequence variability patterns among monomers revealed low, moderate and highly variant domains, indicating that variable levels of evolutionary constraint may act upon the entire monomers. The phylogenetic inference based on the different sets of MspI satDNA family for this species shows a broad polymorphism of the individual monomers, which were distributed into four main clusters. However, such clustering appeared independent from the geographic origin of the nematodes, and could not discriminate isolates or groups of geographically close isolates. Rather, the formation of different phylogenetic groups within this satDNA family suggests an a priori embodying of a set of diverging repeats from a common ancestor satDNA library, which have been differently amplified along the evolutionary pathway of this species. The present work improves knowledge on the evolutionary dynamics of satDNA at the intraspecific level, and provides new information on satDNA sequence variability among natural populations sampled at a local geographic scale.
Bibliographical noteFunding Information:
This work was partially supported by the COST Action 872 NEMAGENICS (‘Exploiting genomics to understand plant-nematode interactions’) and the EC 7th Framework project REPHRAME (KBBE.2010.1.4-09, ‘Analysis of the potential of the pine wood nematode (Bursaphelenchus xylophilus) to spread, survive and cause pine wilt in European coniferous forests in support of EU plant health policy’).
- Pinewood nematode
- Satellite DNA library
- Sequence variability